//! Blinks an LED
 //!
 //! This assumes that a LED is connected to pc13 as is the case on the blue pill board.
 //!
 //! Note: Without additional hardware, PC13 should not be used to drive an LED, see page 5.1.2 of
 //! the reference manual for an explanation. This is not an issue on the blue pill.
 
 #![deny(unsafe_code)]
 #![no_std]
 #![no_main]

 use panic_halt as _;
 use nb::block;
 use cortex_m_rt::entry;
 use stm32f1xx_hal::{pac, prelude::*, timer::Timer};
 
 #[entry]
 fn main() -> ! {
     // Get access to the core peripherals from the cortex-m crate
     let cp = cortex_m::Peripherals::take().unwrap();
     // Get access to the device specific peripherals from the peripheral access crate
     let dp = pac::Peripherals::take().unwrap();
 
     // Take ownership over the raw flash and rcc devices and convert them into the corresponding
     // HAL structs
     let mut flash = dp.FLASH.constrain();
     let rcc = dp.RCC.constrain();
 
     // Freeze the configuration of all the clocks in the system and store the frozen frequencies in
     // `clocks`
     let clocks = rcc.cfgr.freeze(&mut flash.acr);
 
     // Acquire the GPIOC peripheral
     let mut gpioc = dp.GPIOC.split();
 
     // Configure gpio C pin 13 as a push-pull output. The `crh` register is passed to the function
     // in order to configure the port. For pins 0-7, crl should be passed instead.
     let mut led = gpioc.pc13.into_push_pull_output(&mut gpioc.crh);
     // Configure the syst timer to trigger an update every second
     let mut timer = Timer::syst(cp.SYST, &clocks).counter_hz();
     timer.start(1.Hz()).unwrap();
 
     // Wait for the timer to trigger an update and change the state of the LED
     loop {
         block!(timer.wait()).unwrap();
         led.set_high();
         block!(timer.wait()).unwrap();
         led.set_low();
     }
 }   
